The effects of a simulated harvest on Porphyra (Bangiales, Rhodophyta) in South Africa

In South Africa, Porphyra has, until recently, been little exploited, havin g been harvested only for a small health-food market. However, the advent o f land-based abalone farming has increased the pressure on wild Porphyra po pulations, as Porphyra is in demand for abalone fodder. This paper reports on the effects of a simulated harvest on Porphyra populations and those of sympatric fauna. Harvesting, starting in autumn, was found to reduce the bi omass of Porphyra, an effect detectable up to six months later. Porphyra ha d a patchy distribution, with patches having a mode of approximately 300 th alli m(-2). The main effect of harvesting was the removal of patches, as me an thallus size changed little in response to harvesting. Nine months after the start of the experiment, control populations had been reduced, through loss of patches, to the level of treatment populations. Although harvestin g Porphyra reduced populations of some sympatric fauna (amphipods, isopods and littorinid snails), natural Porphyra population decreases had a compara ble effect. Some recommendations are discussed for the management and contr olled harvesting of Porphyra populations in South Africa.